1. Field of the Invention
Embodiments of the invention generally relate to an ultraviolet (UV) cure chamber. More particularly, embodiments of the invention relate to methods and apparatus for providing a uniform UV radiation irradiance profile across a surface of a substrate placed in the UV cure chamber.
2. Description of the Related Art
Materials with low dielectric constants (low-k), such as silicon oxides (SiOx), silicon carbide (SiCx), and carbon doped silicon oxides (SiOxCy), find extremely widespread use in the fabrication of semiconductor devices. Using low-k materials as the inter-metal and/or inter-layer dielectric between conductive interconnects reduces the delay in signal propagation due to capacitive effects. The lower the dielectric constant of the dielectric layer, the lower the capacitance of the dielectric and the lower the RC delay of the integrated circuit (IC).
Current efforts are focused on developing low-k dielectric materials, often referred to as ultra low-k (ULK) dielectrics, with k values less than 2.5 for the most advanced technology needs. Ultra low-k dielectric materials may be obtained by incorporating air voids within a low-k dielectric matrix, creating a porous dielectric material. Methods of fabricating porous dielectrics typically involve forming a “precursor film” containing two components: a porogen (typically an organic material such as a hydrocarbon) and a structure former or dielectric material (e.g., a silicon containing material). Once the precursor film is formed on the substrate, the porogen component can be removed, leaving a structurally intact porous dielectric matrix or oxide network.
Techniques for removing porogens from the precursor film include, for example, a thermal process in which the substrate is heated to a temperature sufficient for the breakdown and vaporization of the organic porogen. One known thermal process for removing porogens from the precursor film includes a UV curing process to aid in the post treatment of CVD silicon oxide films. Current UV curing process is performed by a UV lamp 10 having an elongated UV bulb 12 mounted within a housing 14, as shown in FIG. 8. The housing 14 may include one or more reflectors 16 that face UV bulb 12 and direct UV radiation into a flood pattern 18 over a round substrate 20. While the reflector 16 reflects the majority of radiation that strikes its surface within flood pattern 18, some radiation escapes the reflector surface and falls outside the boundaries of pattern 18 covering the substrate (see FIG. 8). One way to solve this issue is to rotate the UV lamp about the center of the substrate during curing such that the substantially rectangular exposure pattern generated by the UV lamp can compensate for illumination loss at the periphery of the substrate, thereby enhance the uniformity of illumination in the substrate plane. With time, however, the output of this arrangement still produces a large peak at the center of the substrate since the UV radiation at the center is more normal to the substrate, and the UV radiation at the edge is more oblique or weak. While the peak can be somewhat modulated using reflectors (not shown, typically disposed between the UV lamp and the substrate), the film profile of the substrate will still be center high unless the UV radiation is blocked. Blocking the light obviously reduces the overall efficiency of the UV source, which is not desirable.
In addition, the use of the housing 14 and the reflectors may inevitably produce lights that are incident on the surface of a UV vacuum window, which is disposed within the processing region and sealed to the housing 14 to maintain vacuum. The lights travelling through the UV vacuum window are reflected both when going from air to glass and at the other side of the UV vacuum window when going from glass back to air. The amount of light reflected is known as the “reflection loss,” which also negatively affects the center to edge treatment non-uniformity on the substrate.
Therefore, there exists a need in the art for a UV chamber that can be used to effectively cure films deposited on substrates while improving the film uniformity and the throughput.